Any circuit operating at high voltage is subject to voltage breakdown at higher elevations (lower atmospheric pressure conditions). Such voltage breakdown is often harmful to the equipment involved. One solution to the problem is to use sufficiently higher quality components so that either breakdown does not occur at elevations of interest or that such breakdown causes no harm. In some situations equipment need not operate at higher altitudes, but need only "survive".
An airborne weather radar is an example of such equipment. Specifications require that it must operate at relatively lower altitude after being on, but not necessarily operational, at higher altitude. It is becoming common to utilize ordinary television sets as the display portion of the radar. A television set contains a high voltage flyback transformer which is subject to damage at high altitudes (low pressure) conditions.